1. Field of the Invention
The main object of the present invention is an electrical circuit testing device and a circuit comprising the said device.
The present invention pertains chiefly to tests on the correct functioning of electrical circuits such as, for example, digital and/or logic circuits. It can be used to detect the malfunctioning of an integrated circuit, a printed circuit or any other electronic device. Once the malfunction is detected, measures can be taken to reduce the consequences of the malfunction to the minimum. For example, the malfunctioning electrical circuit may be replaced, or the result given by the said circuit may be ignored.
2. Description of the Prior Art
The increasing complexity of electronic circuits is making it increasingly difficult to test these circuits exhaustively so as to detect all malfunctions with certainty. There are known methods of conducting tests with very high chances of detecting a malfunction in a circuit. In particular, in one prior art method, sequences of long pseudo-random vectors are injected into the digital and/or logic circuit. The long pseudo-random sequences are obtained by re-looping certain cells of a shift register through an exclusive-OR gate. By using Nth degree generating polynomials, sequences with a length of 2.sup.N -1 can be obtained.
At the output of the device to be tested, it suffices to verify that the results obtained conform with those that should be given by a board in good working order. For example, the result obtained is compared with those given by a board which is known to function perfectly, or else with results obtained by simulation.
An improved method consists in using signature analysis. This method is called the BILBO method. Another shift register is connected to the output of the device to be tested. Certain cells of this shift register are re-looped through an exclusive-OR gate. This second shift register, provided with its exclusive-OR logic gate, makes it possible to compress the data obtained. At the end of the test, it suffices to compare the contents of the shift register with those that would be obtained for a device in perfect working order to ascertain, with very high efficiency, that the tested device is malfunctioning or not malfunctioning.
The prior art type of device has the disadvantage of not conducting tests on the input/output bus of the device.